Homework Help:
Magnitude of force

A 1904kg car is pulling a 580.72kg trailer. Together the car and the trailer have an acceleration of 2.32m/s^2. Neglecting frictional forces acting on the trailer, find the magnitude of the force exterted on the car by the road.

My prof told me to just add the two masses and multiply them the acceleration. The answer was wrong. But since it's only asking about the force regarding the car, could we just neglect the trailer's mass? Wouldn't it just be 1904(2.32)?